Refractory metal product and process of making the same



AU 223 EX Oct. 9, 1923.

c. A.. I AlsE REFRACTORY METAL RODUCT AND PROCESS 0F MAKING THE SAME` Filed may 2,: 1921 2 Sheets-Sheet l INVENTOR C/emem/La/S ya METALLURGY,

Oct. 9 C. A. LAISE REFRACTORY METAL PRODUCT AND PROCESS QF MAKING- vTHE SAME Filed May 2, 1921 2 Sheets-Sheet' 3 Kyi 4 KM? l y 7g 7p ,La 7l /1 52 l l f ffv S f2 "//`/`///`/'7/// F5.. MMALLUHUY,

Patented Uct. 9, 1925.

UNITED STATES PATENT OFFICE.

REFRACTORY METAL PRODUCT AND PROCESS 0F MAKING THE SAME.

Application led May 2,

To @ZZ whom t muy concern.:

Be it known that I, CLEMENS A. LAIsE, a citizen of the United States, and a resident of lVeehawken, county of Hudson, State of New Jersey, have invented certain new and useful Improvements in Refractory Metal Products and Processes of Making' the Same, of which the following is a specification.

The present invention relates to electric contact elements, particularly for vibratoryy circuit making and breaking devices which have come into use to a very large extent in recent years and also for the method of making these devices.

The invention particularly consists of such a device made from fused or molten refractory metal, such as tungsten or molybdenum or the alloys of these t-wo metals.

More particularly does the invention relate to an elect-ric contact element made of fused and molten tungsten and to the method of making the same.

Nature has given to mankind the element tungsten which was discovered by Sheele about the year 1781. The French scientist, Henry Moissan, was the first to publish the fact that under certain conditions tungsten when heated was malleable and could be forged and worked.

Two Austrians, Alexander Just and Franz Hanaman, are credited with being among the first to produce an incandescent lamp in which the tilamentary body is made of tungsten, and William D. Coolidge, later, by a particular process Worked out by him, produced a wire of tungsten metal which was pliable and which could therefore be readily placed into lamps and used as the filamentary body.

It is therefore seen that various forms of tungsten metal are known, each form being produced by a particular process, but I find that none of these processes is adapted to produce a tungsten material which is particularly suitable for electric contact manufacture and use. The reason for this fact is that the tungsten produced by each of the processes when used for face plates for electric contacts has a tendency t-o produce such contacts which pit and disintegrate after comparatively short use, and especially are 1921. serial No. 466,336.

the old forms of tungsten heretofore used for this purpose unsuitable and inoperative for magnetos under conditions where the sparks produce higher temperatures.

The forms of tungsten heretofore produced for contact purposes are not sensitive enough for these purposes, since they are not soft enough and are not of a suliiciently high electric conductivity. For these reasons platinum and platinum iridium alloys still have to be used despite their high cost of manufacture.

The metal tungsten has not been so satisfactory as it might be because] of the nature and manner in which the metal has heretofore been treated and produced. I have discovered that the best quality of electric contact is produced from the densest tungsten material possible, namely, from molten or fused tungsten. Thus, a tungsten disc possessing a very dense structure in which the particles consist of very tine grained and compact units, has the highest electrical conductivity and is best suited for this purpose.

The very nature of the manufacture of tungsten rods and slabs at the present time hinders the production of such a material,

Y for it is started with a coarse powder, which powder is pressed into an ingot, then baked and afterwards sintered by making the ingot the conducting medium in a chamber through which hydrogen is flowing.

In carrying out this process of the art, owing to the radiation and conduction of the hydrogen, a very decided difference of temperature is produced between the outside surface of the slug or ingot and the inner or central portion thereof which may otherwise be termed its core. This is established by the very fact that whenever the tungsten ingot is so treated near toy its fusing point, the tungsten fuses together on the inside and thus a hollow core is formed. Therefore, the sintering operation is usuallyv carried out by passing through it a current which is approximately 85 to 95 per cent of the current necessary to fuse the tungsten. The very nature of all known processes of manufacture of refractory contact materials, such as tungsten, is such thatA a more or less porous material is produced which is neither as compact nor as dense as it would be if it were produced of fused or molten metal.

It has been found that the walls of tubes made of sintered tungsten are porous, which fact is established by trying to create a yacuum in these tungsten tubes.

To overcome these difficulties, I have developed a process whereby a contact ma terial of tungsten is produced from fused or molten tungsten or fused oi molten tungsten and molybdenum alloys, which material I have found to give much better results for contact purposes. Furthermore, my process is so simplified that this fused or lnolten inaterial can be produced at much less cost than that necessary to produce tungsten heretofore used in the art for contact purposes.

Contrary to the practice adopted in the artin the manufacture of tungsten commonly known as wrought or ductile tungsten. I iind that it is necessary to use as the basis of my starting material a particularly fine crystalline material, and this is so whether the material be tungsten or molybdenum or tungsten molybdenum alloys.

After this very fine crystalline material has been compacted into a metallic ingot, I subject it to external heat treatments to bring it to its fusing point, rather than to internal heat treatments, which latter is the case when current is sent through the ingot. I force the heat from the outside to the inside, thus fusing the outside of the slug, which results in slugs haring no hollow core. li'ith pure tungsten this heat treatment is accompanied by means of an arc or by combining pressure and external heat. 'hen the product is a tungsten molybdenum alloy. the particles are so compact and dense that they form an excellent contact material, and I find that the proportions of the two metals which are desirable to be used in the making of such an alloy is proportioned at the rate of about 80 per cent; tungsten to Q0 per cent of molybdenum.; As molybdenum has the next highest melt-f ing point to tungsten and as it belongs to the same periodic group, it follows thatmolybdenum is the most logical metal to be used with tungsten when an alloy of this nature is desired` the alloy thus haring a slightly lowei` melting point than tungsten.

As tungsten is the most desirable metal to be used for the manufacture of electric contacts, this description will be confined to this metal, though it is to be understood that the metal molybdenum or alloy. as above specified, of tungsten and molybde num, may also be used and treated in accordance with the process hereinafter described for the purpose of manufacturing electric contacts from these materials.

In describing my process I will refer to the accompanying drawings which illustrate in general the different pieces of apparatus which I find suitable to employ in carrying out the process.

In the drawings:

Fig. l illustrates an, eraporating dish.

Fig. 2 is a reduction furnace.

Figs. 3 and et illustrate various forms of molds.

Fig. 5 is a sintering furnace.

Fig. G is an end View of a Iiennerfelt arc furnace for fusing or melting the material.

Fig. 7 is a side view .partly in section of the same.

Figs. 8 and 9 are details in section to illustrate steps in my process.

Referring now particularly to the tungsten metal, the starting material for producing my contact substance is a tungstic acid which has been purified so that it is chemically pure IVO, containing not more than 0.25 per cent of mineral impurities. This tungstic acid is dissolved by slowly introducing 1,00() grams of the same into a mixture of 1,00() c. c.'of chemically pure ammonium hydrate sp. gr. 0.90() and 2.50() c. c. distilled water. After stirring the same for half an hour most of the IVO., is dissolved and the ammonium tungstate solution is filtered. This solution should then have a clear water colored appearance with just a tinge of yellow color.

The ammonium tungstate solution is then placed into a porcelain eraporating dish A, and about 50() c. c. of C. P. HCL is permitted to run into the dish from fine constrictions with constant stirring, until the solution begins to get turbid and very ne crystals begin to oat around in the same. Silica tube immersion heaters B and B are then introduced into the dish A. as shown in Fig. 1, and the solution is c 'aporated to approximately 3/4 of its original bulk. The heaters are then taken out and the liquid is allowed to cool toi room teniperature. The resultant crystals produced by the combined action of salting out and evaporation haring a very fine needle like structure particularly suitable for the production of my materials. These crystals are then allowed to settle; the mother liquor is poured ott' and the crystals are washed several times with distilled water and then filtered through a Buchner vacuum funnel and dried in a nickel pan in a gas furnace heated to about 300 to 400 degrees C. for a sufiicient length of time so that most of the ammonia is driven oif, but still containing some undecomposed ammonium tungstate. the color haring now a tinge of green rather than pure yellow, the substance containing about 98 per cent IVO, and 2 per cent to l per cent of NH3.

As above mentioned, in order to produce a METALLURGY,

final product possessing the characteristics particularly adapted for contact use and manufacture, I must start with a non-crystalline metal of exceedingly fine structure. For this purpose I have developed a new type of reduction furnace shown in Fig. 2, whereby the hydrogen gas passes through the material to be reduced rather than over it as heretofore, and the moisture is carried out of the metal zone as soon as the hydrogen has combined with the oxygen instead of being carried over the metal and making it crystalline.

The furnace consists essentially of a porous alundum tube 10 against the walls of which abuts a resistance heat coil 11 consisting of approximately 10 feet of #22 Rayo or nichrome wire and operating on a 220 v. circuit. This tube is surrounded by a 200 mesh nickel gauze basket, or a 200 mesh nickel-chronic alloy wire gauze basket 12, resting on supports 13 and extending to the top of the furnace. These are all enclosed in a container 14 of pyreX-glass or silica having a cover 15 provide-d with holes 15 for the escape of the gas.

The heater is connected in circuit by means of a line 1'6 having wires 17 and 18 passing between the porous tube 10 and support 19, the cap 20 being so constructed as to also contain a conduit 21 through which the hydrogen or reducing gas may pass from the pipe 22 into the apparatus so that it may further pass through the )Valls of the porous tube 10 into the basket 112 in order to come into contact with the heated material M contained in the basket and escape through the holes 15. I may also provide a wire heating coil upon the outside, as at 25, in order to concentrate same.

About 500 to 7 50 grams of the above W03 powder are placed in the nickel or nickelchrome wire basket. The porous alundum tube is carefully closed andmade non-porous on top. The reducing gas, such as hydrogen or mixed with ammonia gas, passes through the furnace and since the tube is tightly closed on top and non-porous on top, the `gas is forced through the wall of the alundum tube through the material to be reduced and through the gauze basket and out of the openings 15. The flow of current through the heating coil is regulated by means of a rheostat so that the walls of the alundum tube attain a temperature of approximately 100 degrees C., in a period of approximately one half hour. The current is then increased and the temperature raised from 600 to 700 degrees C., and held at that temperature for about two hours and then the temperature is increased to 900 degrees to 1000 degrees C., and held there for about four or five hours` at which time the reduction is complete. The furnace is then permitted to cool, The heating tube is then lifted out and the basket containing the reduced material is also removed and the metal is sifted through a 200 mesh sieve and is now ready for use.

Since all of the hydrogen used in this method comes in contact with material to be reduced, the gas is used much more efficiently than in any other process of which I am aware and a quicker reduction can be effected.

It should be stated that the flow of gas should be about 10 to 15 cu. ft. per hour when the small reduction unit is used and with a quick flow of gas the above reduction schedule can be reduced considerably.

I find also that iron and nickel may be reduced in the manner above set forth with excellent results, the latter being used for catalizing purposes.

The reduced metal, as above obtained, which is light, fine and sticky, after being sifted is ready to be formed into ingots. This is done by taking the metal molds C and C', as shown in Figs. 3 and 4C, then forcing the metal in by applying pressure thereto by means of a plunger and arbor press. I find that it is preferable to place substantially 200 grams of material into a mold having a hole Z of 3/8 in diameter, or one which is 3/8 square as at d. The

mold .is made of nichrome or other nickelj chrome alloys, and I find it is especially desirable before using the mold to heat the same in air so that it will become coated with a thin film of chromium oxide. The mold is made of two parts 28 and 24, 25 anc 20 and is held together' by clamps 27 which may be suitably joined at 28 in any well known way. After pressing the powder into the mold it is then placed in a furnace. A stream of hydrogen is continually flowing through this furnace and the mold which is placed therein is subjected to a temperature of 1100 to 1300 degrees C., for approximately one-half hour, after which the mold containing the slug or ingot is cooled in an atmosphere of hydrogen.

In the prior art the metal powder is Hrst placed in a mold and compacted into a slug by pressing the same in a hydraulic press under very great pressure, removed therefrom and subsequent-ly heated.

In contradistinction to this, in the carrying out of my process I use the abo-ve mentioned mold of nickel-chrome alloy and before using the mold it is preferably coated with chromium oxide. The metal powder is then packed in the mold and is subjected, together with the. mold, to the above mentioned heat treatment. 'Since the nickelchromium alloy mold has a low coefficient of expansion it exerts a pressure upon the metal powder therein so that the material in the mold is subjected to the combined action of heat and pressure, and consequently after cooling the metal or alloys are removed from the mold in a compact form, i. e., a slug or iugot possessing a metallic clang.

As the chromium oxide on the surface of the mold is not reduced in hydrogen and does not combine with the ingredients of the metals being molded, the easy removal of the slug from the mold is permitted. I am thus able to produce metallic ingots from powder` which possess a very fine structure which could not have been pressed up into a body by the methods now known in the art without the use of a binding material.

Through this combined action of pressure and heat the metal is compressed into a compact sintered slug having metallic ring. Such a heat treatment of one-half an hour is usually sufcient, for upon opening the mold after such a treatment it will be found that the metal has been converted by this treatment into a compact sintered ingot. This sintered slug. ingot or rod is then placed into a high temperature heat treating furnace, as shown in Fig. 5. This furnace consists essentially of a refractory metal tube or slab of tungsten ortungsten alloys which has a stationary water cooled copper electrode 5] attached to one end, and a movable water cooled copper electrode 52 attached to the other end so as to allow for.,V the expansion or contraction of the metal tube or slab .30 during the heat operation.

The ends of the tungsten tube 50 lit into the water cooled copper electrodes 51 andi 52. as shown, to which the main leads and -L are attached, these leads being con-i' nected in circuit to a transformer 55, con-V The entire chamber 1s' through the opening G5,the refractory metal slab or tube being supported by refractory metal rods 6G of the same material as the heat element. The ingots to be fused are allowed to remain in the heating element after it has reached it-s maximum temperature exceeding 2700 degrees C., for about Q0 minutes or until the volume of a given weight of the slug has been reduced by about 1S to Q5 per cent; that is, the heat treatment has produced a fusing effect sullicient to increase the density of the ingot by 18 to per cent. The current passing through the heating element is then interrupted, the fused slug is shoved into the water cooled chamber 67 by means of a tungsten rod and then removed through the opening GS. The operation is carried out in an atmosphere of hydrogen or in a low pressure hydrogen vacuum. In the latter case long rubber stoppers are placed into each end and the chamber is evacuated through a glass tube in one of these rubber Stoppers.

By this procedure the entire slug is subjected to the same treatment and there is no loss due to untreated ends. The slug being heated by external means does not form blow holes in the center and a much more compactmass is therefore obtained.

Slugs subjected to the above treatmentl after being fused to 8() per cent of their original volume are in a suitable condition for mechanical working.

In the event that the fused ingot is made of a tungsten and molybdenum alloy, the slug is ready for mechanical working, but 'when the ingot is made only of tungsten, then before subjecting it to mechanical working I subject it to a further heat treatment, as follows:

The further fusing of this metallic ingot is then carried on by means of a special arc furnace 70, using the Rennerfelt arc principle1 as shown in Figs. 6 and 7, which furnaces are provided with carbon electrodes Tl. The slug S to be fused rests upon a frame 72 made of tungsten blocks or rods resting upon an insulating base 73. The furnace may be constructed of refractory insulating material, such as magnesia and fire clay bricks, and I have found that a suitable way of placing the slug S into position for fusing is by means of another slug of tungsten S operated through the side of the furnace.

In the use of the furnaces as shown in Figs. 6 and 7 the heat is forced into the tungsten slug either in air or in an atmosphere of hydrogen so that maximum temperature is produced 0n the exterior of the slug rather than in its interior. The slug S being attached to the refractory metal rod S can be moved back and forth in the are and if necessary, can be revolved in the arc at the same time, the rod S being used as a handle for that purpose. This manipulation is possible because the ends of the, slug to be fused are supported on the refractory metal frame 72 and this frame may be electrically heated by means of an alternating current through the circuit 75 iudicated in Fig. 7.

As above stated, the arc in these furnaces is directed downward and the material being held in the zone of maximum heat is effectually fused, and notwithstanding the fact that the electrodes are carbon. we find that the material being fused in such a furnace i5 free from carbon. The rod when composed of tungsten is now in condition to be mechanically worked.

Owing to the fact that refractory metals such as tungsten readily absorb oxygen. the

,surface thereof oxidizes in the air and if lheated slowly therein in a slightly oxidizing atmosphere, a hard compact coating of Mi ET ALLU RGY,

oxide forms on the surface, which compact coating having a very low coefficient of expansion, exerts a tremendous, pressure on the metallic core and actually brings the metallic core to a state of fusion at an external temperature far below the temerature of the melting point of the metal itself when under normal pressure.

As an illustration of this fact, I have taken pieces of tungsten .060 and .050 in cross sect-ion and about 5 long, which were brittle, and have subjected them to heat treatment in a slightly oxidizing atmosphere at about 1000 degrees C., for ten hours, thereby coating them with a firm coating of oxide 83, as illustrated in Fig. 9, and upon removing them from this heat treatment we have found the ends of the tungsten metal fused and after removing the coating of oxide we found that the tungsten body which before treatment was brittle, was now quite ductile and pliable.

In order to effect-a slow oxidation, the oxidizing atmowhere may consist of nitrogen with five per cent or less of oxygen.

The pressure may be still furthe-r increased by placing the tungsten body in an outer sleeve 84 of a. nickel-steel or refractory metal of l'ow coefficient of expansion,

as illustrated in Fig. 8, this sleeve then surrounding the tungsten body l/V. Upon heating the composite body, either in air or in an oxidizing atmosphere, oxygen will be absorbed by the inner core which will form a strata of oxide between the inner core and the wall of the covering, which upon building up exerts a pressure on the outer covering and in turn upon the inner metallic core, thereby bringing the same to a state of fusion at a lower temperature.

Therefore, as an alternative, instead of fusing the tungsten slug in the furnace illustrated in Figs. 6 and 7, I subject the rods which have been fused in the furnace shown in Fig. 5, to a combined pressure and heat treatment, as above described,

thereby producing a compactly fused metal rod. The oxide may then be mechanically removed and also dissolved off by means of a boiling solution of caustic soda.

Tungsten slugs prepared by any of the above methods and which have been fused to less than 85 per cent of the original volume may now be mechanically hammered, rolled or swaged.

In order to reduce oxidation of the slugs or rods to a minimum during the mechanical working, I first dip them into a thin paste 0f chromium oxide and crude oil and then bake the oxide onto the metal in an atmosphere of hydrogen at 1200 degrees C., to 1300 degrees C., in an electric furnace. After repeated baking, a fine protective layer of oxide is formed on the ingot or rod.

I may also attain this result by dipping the slug into molten nickel-chromium alloy. A thin layer of alloy forms on the surface after heating in air, the chromium is oxidized and the nickel is then distilled off at a high temperature, leaving the chromium oxide upon the surface of the body.

Like all metal working operations, the metal bars are first worked hot, as is the case when working steel, platinum-iridium, nlickel-chromium and other refractory meta s.

Since tungsten is rather sensitive to sulphur or any other impurities that may be in illuminating gas, and especially since high temperatures are desirable, I always heat and anneal my metal bars in special Oxy-hydrogen blast furnaces. By this means the detrimental effects of illuminating gas are avoided and the malleability and ductility of the met-als is not impaired.

After the slugs have attained a temperature 0f 1500 degrees C., they are placed under a. 100 lb.` hammer and subjected to a few blows at a time so that the hammering never takes place after the tempera-ture has been reduced to about 1200 degrees C.

After the bars have been hammered down to a thickness of 3/16 to 1/8 they are examined and in case cracks have developed on the edges or faces, these are removed by grinding.

The flat plates, heated to 1500 degrees C., are then rolled on 4 or 6 chilled cast iron rolling mills, so that the velocity of the material passing through th-e rolls is from 60 to 7 5 feet per minute. Reduction drafts of .002 to .0025 are taken.

The plates are rolled to 1/64 above the required thickness. They are then cleaned by treating in hydrogen at 1100 degrees C., and cooled in hydrogen. The split ends and cracks on the sides are cut off and the reduced oxide on the metal is removed b scratch and emery cloth wheels. The meta is th'en rolled to the final thickness the same as above.

If sheets under .030 in thickness are desired, the temperature of rolling is reduced to 1100 degrees C., and reduction drafts of .002 are taken until the thickness reaches .020. The working temperature is then reduced to 600 degrees C., and rolling is done on a 5 carbon-chrome steel roll operating at 20 R. P. M. After reaching a thickness of..012 the rolling is done practically cold with intermediate annealing of the material in a hydrogen furnace at 1150 degrees C., for five minutes.

If round rods are desired, the material is first hammered at 1500 degrees C., on a swaging machine using high speed steel swaging dies. After being reduced to 3/16 diameter the round rods are swaged at a temperature below 1100 degrees C., taking reductions of about 10% to 15% per pass, the

material being guided through a furnace in front of the machine.

The rods are finally finished by swaging the same in hardened tungsten steel, fiat faced dies on the swaging machine, or by drawing the same through hardened high speed tool steel dies, on a draw-bench.

For some purposes I prefer to leave the chromium oxide on the material to be worked so that it is mechanically worked into the body. I then find that such coated bodies are excellently suited for high temperature electric heating elements.

If the above material is to be used for contact purposes, I prefer to clean the surface of the sheet or rod, by boiling it in a hot caustic solution, and then anneal it in an atmosphere of hydrogen at 900 degrees to 1000 degrees C., for about ten hours,there by relieving all the strains in the material, and producing a soft and more malleable product.

The fused or molten material which has a very fine grained structure is now in a condition to be applied to the manufacture of products useful in the arts.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. An article of manufacture comprising dense. compact, fused tungsten which has been heated while confined in a mold of refractory material of lower' coefficient of expansion.

2. An article of manufacture comprising dense, compact, fused tungsten which has been heated and sintered while confined in a mold of refractory material of lower coefficient of expansion.

3. An article of manufacture comprising dense, compact, fused tungsten which has been heated and sintered while confined in a mold of refractory material of lower coefficient of expansion and fused.

et. An article of manufacture comprising dense, compact. fused tungsten which has been heated and fused while confined in an envelope having a lower coefiicient of expansion.

5. An article of manufacture comprising dense. compact, fused refractory metal which has been heated and fused while confined in an envelope having a lower coefficient of expansion.

0. The herein described process which comprises packing refractory metal powder of high melting point in a nickel chrome mold and heating said mold sufficiently to form an ingot of said metal.

7. The herein described process which comprises packing` powdered tungsten in a nickelchrome mold coated with chromium oxide and heating said mold sufiiciently to form an ingot of tungsten.

8. The herein described process which comprises packing refractory metal powder of high melting point in a nickel chrome mold coated with chromium oxide and heating said mold sufficiently to sinter said metal powder to produce a coherent body, and subsequently subjecting said body to a sintering and fusing temperature.

9. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufficiently to sinter said powdered tungsten into a coherent body and subsequently subjecting said body to a sintering and fusing temperature.

10. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold and heating said mold sufficiently to form an ingot of tungsten and subsequently subjecting said ingot to a temperature above 2700 degrees C.

11. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heat-ing said mold sufficiently to form an ingot of tungsten and subsequently subjecting said ingot to a high temperature until its volume has been reduced about 1S to 25 per cent.

12. The herein described process which comprises packing powdered tungsten in a hot nickel-chrome mold and subsequently heating said mold sufficiently to form an ingot of coherent tungsten and subsequently subjecting said ingot to a sintering` and fusing temperature in an atmosphere of hydrogen.

13. The herein described process which comprises packing powdered tungsten in a hot nickel-chrome mold and subsequently heating said mold sufficiently to form an ingot of tungsten and subsequently applying external heat to said ingot to increase its temperature above 2700 degrees C.

11. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufficiently to form an ingot of tungsten and sebstajuently applying external heat to said ingot to in crease its temperature above 2700 degrees C. in the presence of hydrogen.

15,'1`he herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufficiently to form an ingot of tungsten and subsequently applying external heat until its volume is reduced about 18 to 25 per cent.

16. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufficiently to form an ingot of tungsten and subsequently subjecting said ingotto a high temperature loo 75g lVlElALLURGY,

sten by means of an electric arc produced from carbon electrodes.

18. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufiiciently to form an ingot of tungsten and subsequently subjecting said ingot to a high temperature until its volume has been reduced about 18 to 25 per cent, and then fusing said tungsten by heat applied to the outside thereof.`

19. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufficiently to form an ingot of tungsten and subsequently subjecting said ingot to a high temperature until its volume has been reduced about 18 to 25 per cent, and then fusing said tungsten by using it as an electric arc electrode.

20. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufficiently to form an ingot of tungsten and subsequently subjecting said ingot to a high. temperature until its volume has been reduced about 18 to 25 per cent, and then fusing said tungsten by using it as an electric arc electrode in the presence of hydrogen.

21. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufficiently to form an ingot of tungsten and subsequently subjecting said ingot to a high temperature until its volume has been reduced about 18 to 25 per cent, and then fusing said tungsten by using it as an electric arc electrode in the presence of hydrogen at very low pressure.

22. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufficiently to form an ingot of tungsten and subsequently subjecting said ingot to a high temperature until its volume has been reduced about 18 to 25 per cent, and then slowly heating it in an oxidizing atmosphere.

23. The herein described process which comprises packing' powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufficiently to form an ingot of tungsten and subsequently subjecting said ingot to a high temperature until its volume has been reduced about 18 to 25 percent, and then slowly heating it in an oxidizing atmosphere to about 1000 degrees C. for about ten hours.

24C. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufficiently to form an ingot of tungsten and subsequently subjecting said ingot to a high temperature until its volume has been reduced about 18 to 25 per cent, and then slowly heating it in an oxidizing atmosphere and removing therefrom the coating of oxide thereby formed.

25. The herein described process which comprises placing an ingot of dense tungsten in a sleeve of refractory metal having a low coefficient of expansion, and heating.

26. The herein described process which comprises placing an ingot of dense tungsten in a sleeve of refractory metal having a low coefficient of expansion, and' heating in an oxidizing atmosphere.

27. The herein described process which comprises placing an ingot of dense tungsten in a sleeve of refractory metal having a low coefficient of expansion and heating in an oxidizing atmosphere sufficiently to fuse said tungsten after an oxide has been formed on said ingot.

28. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold suiiiciently to form an ingot of tungsten and subsequently subjecting said ingot to a high temperature until its volume has been reduced about 18 to 25 per cent, and then fusing said tungsten by a combined heat and pressure treatment.

29. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufficiently to form an ingot of tungsten and subsequently subjecting said ingot to a high temperature until its volume has been reduced about 18 to 25 per cent, cooling, dipping said ingot into an oxide paste and baking it.

80. The herein described process which comprises packing powdered tungsten in a nickel-chrome mold coated with chromium oxide and heating said mold sufficiently to form an ingot of tungsten and subsequently subjecting said ingot to a high temperature until its volume has been reduced about 18 to 25 per cent, cooling, applying chromium oxide to said ingot and subjecting it to metal working operations.

81. The process of producing fine7 compeet fused tungsten which consists in subjecting ne tungsten powder to J combined heat und pressure treatment in n nickelehromium alloyv mold und subsequently 'fusing the ingot thus formed to substantially S5 per cent otl its volume by means ot' an external heat treatment in u hydrogen atmosphere of low pressure. 1

32. The process of producing n line com` pact fused tungsten by subjectingp` line tungsten powder to n combined heut and pressure treatment in a nickel-chromium alloy mold and subsequentlrY 'fusing the ingot thus formed to substantially 85 pel' cent of its volume by means ot :in external heut trentlnent in :1, hydrogen atmosphere o" low pressure and finally by means of :i combined heut and pressure treatment exerted by a dense oxide coating in en atmosphere containing a small percentage otf oxygen.

The herein described process which consists in subjectingl :1n ingot olf dense compnettune'sten to heat in un oxidizingr zitmosphere, therebyv producing u compnet coating ot' oxide on the surlnce of the ing'ot olf lower c eliicient ot expansion than that of the metal ingot which upon continued heutnze,` subjects the core to combined heat :ind pres sure.

ln witness whereof l here hereunto set my hund nt the borough olf Manhattan, city und #Stute ol New York, this 29 day olf April, 1921.

CLEMENS A. LAISE. In presence olum lsAnnL R. FLETCHER. 

